Calibration System for an Energy Beam of an Additive Manufacturing Device

The present invention relates to a calibration system and a method and use of a calibration aid for calibrating an energy beam.

Additive manufacturing processes are becoming increasingly relevant in the production of prototypes and now also in series manufacture. In general, “additive manufacturing processes” are manufacturing processes in which a manufacturing product or component is built up by depositing material, usually on the basis of digital 3D design data. The structure is usually created by applying a build-up material in layers and selectively solidifying it. The term “3D printing” is often used as a synonym for additive manufacturing; the production of models, samples and prototypes using additive manufacturing processes is often referred to as “rapid prototyping”, the production of tools as “rapid tooling”, and the production of series products as “direct manufacturing”.

The selective solidification of the build-up material is often achieved by repeatedly applying thin layers of the usually powdery build-up material on top of each other and solidifying them by spatially limited irradiation using an energy beam, e.g. by means of light and/or heat and/or particle radiation, at the points that, after manufacture, are to form part of the manufactured product to be produced. An example of a method that works with irradiation is “laser powder bed fusion” or “selective laser melting”. The powder grains of the build-up material are partially or completely melted during the solidification process with the help of the energy introduced locally at this point by the radiation. After cooling, these powder grains are then bonded together in the form of a solid.

In this type of production, it is often necessary for a process gas to be passed through the process chamber for inertisation, cooling or removal purposes (in particular with a fan). This means that the additive manufacturing process takes place under a process gas atmosphere that differs in its properties—possibly significantly—from the normal ambient atmosphere. For example, the process gas atmosphere may have a lower humidity content than the normal ambient atmosphere.

Sometimes it is necessary to calibrate the energy beam in order to optimise the properties of the energy beam for manufacture. To do this, a measuring instrument is inserted into the beam path that records the measured values for certain beam properties of the energy beam. In order to provide the same atmosphere as in additive manufacturing for calibration, the entire process chamber is usually flooded with the process gas for calibration. This is particularly time-consuming if several calibration steps have to be carried out and/or the process chamber first has to be brought back to a normal ambient atmosphere in order to open it safely.

The problem addressed by the present invention is that of simplifying the calibration of an energy beam of an additive manufacturing device.

This problem is solved by a calibration system according to claim, a method for calibrating an energy beam according to claim, and the use of a calibration aid for calibrating an energy beam according to claim.

The aforementioned calibration system for an energy beam of an additive manufacturing device comprises an additive manufacturing device with a beam inlet for the energy beam. It also comprises a gas supply for providing a gas that is suitable for calibration, a measuring unit for detecting a beam property of the energy beam and a calibration aid with a hollow space and an inflow opening for introducing the gas into the hollow space. The calibration aid is arranged in the additive manufacturing device in such a way that the energy beam is surrounded by the hollow space from the beam inlet to the measuring unit, and the gas flows into the hollow space for calibration.

The energy beam is basically any energy beam that is suitable for selective melting or sintering of a corresponding material for additive manufacturing. For example, the energy beam is generated by means of a laser, preferably a CO laser. It can also be a CO2 laser, a diode laser, in particular a diode laser with a wavelength of 4-7 μm, a Nd:YAG laser, an electron beam or the like.

During operation, the energy beam enters the process chamber or the construction space of the additive manufacturing device via the—at least one—beam inlet. The beam inlet can be designed in a simple manner as an opening or aperture in the process chamber.

However, in order to keep the volume of the areas to be filled with process gas small, the process chamber is preferably separated gas-tightly from other areas of the additive manufacturing device, such as an optical chamber for the optical elements for adjusting the energy beam. The beam inlet is therefore designed, for example, as a coupling window that is transparent to the energy beam.

The gas that is suitable for calibration is selected depending on the energy beam, i.e. depending on the type of energy beam. It has at least similar optical properties to the process gas. In the case of a CO laser, dry air or nitrogen is preferably suitable as the energy beam for calibration. The gas is provided, for example, by means of a gas cylinder, a separate in-house gas supply, or preferably by means of the gas supply of the additive manufacturing device.

The hollow space of the calibration aid is surrounded by a hollow body. The hollow body can be formed substantially by corresponding elements of the calibration aid. Alternatively, the hollow body is formed by the interaction of elements of the calibration aid with elements of the additive manufacturing device, such as a wall of the process chamber and/or the coupling window or beam inlet. In this way, the energy beam is simultaneously housed from the beam inlet to the measuring unit or measuring instrument during intended operation. This means that the beam route or beam path of the energy beam is largely surrounded within the process chamber by the beam inlet, the calibration aid and the measuring instrument. It runs through the hollow space of the calibration aid. This means that the beam path in the calibration system is shielded from the ambient atmosphere, which may have properties that would hinder precise calibration. This improves the reproducibility of the calibration.

For calibration, the gas flows or is introduced into the hollow space of the calibration aid through the inflow opening. For this purpose, the inflow opening is fluidically connected to the gas supply, e.g. by means of a hose or the like.

The measuring unit is designed depending on the beam property of the energy beam to be detected. If, for example, the power of the energy beam is measured or detected as a beam property by means of the measuring unit, the measuring unit is designed as a power meter. It is arranged adjacent to the calibration aid and preferably attached to it in such a way that the energy beam impinges on a measuring region of the measuring unit.

The calibration aid is therefore preferably an additional unit that can be easily separated from the additive manufacturing device or removed from the process chamber and is only inserted into the process chamber for the calibration of the energy beam.

Accordingly, the aforementioned method for calibrating an energy beam of an additive manufacturing device comprising a beam inlet has at least the following steps: In one step, a calibration aid is provided, which comprises a hollow space and an inflow opening for introducing a gas that is suitable for the calibration. In a further step, the calibration aid is introduced into the additive manufacturing device so that the energy beam is largely surrounded by the hollow space from the beam inlet to a measuring unit. In a further step, gas flows into the hollow space of the calibration aid. Meanwhile, the calibration of the beam path is carried out in a subsequent step. The measuring unit detects a beam property of the energy beam.

The method therefore substantially comprises the functional features of the calibration system described above. Once calibration has been completed, the calibration aid and the measuring unit are preferably removed from the process chamber in order to be able to carry out additive manufacturing processes using the additive manufacturing device.

As aforementioned, a calibration aid is used in accordance with the invention to calibrate an energy beam of an additive manufacturing device. The calibration aid is inserted with its hollow space into the additive manufacturing device so that the energy beam is surrounded in the hollow space from the beam inlet to a measuring unit. During the calibration of the beam path, a gas that is suitable for the calibration flows into the hollow space of the calibration aid and a beam property of the energy beam is detected by means of the measuring unit.

Compared to flooding the entire process chamber, the use of the calibration aid according to the invention in the process chamber of an additive manufacturing device therefore advantageously reduces the volume into which the gas that is suitable for calibration in order to calibrate the energy beam flows or floods. This reduces the time required for calibration in particular. This is particularly the case if several calibration steps and therefore several floodings are necessary after a new, adapted setting of the energy beam.

Further, particularly advantageous embodiments and developments of the invention can be found in the dependent claims and the following description, wherein the independent claims of one claim category can also be developed analogously to the dependent claims and exemplary embodiments of another claim category and, in particular, individual features of different exemplary embodiments or variants can also be combined to form new exemplary embodiments or variants.

The gas that is suitable for calibration is referred to below as “gas”. Preferably, the gas is fed into the hollow space in such a way that a relative humidity of below 5% is maintained in the hollow space during calibration, particularly preferably below 4%, very particularly preferably below 3%. As described above, the relative humidity is relevant for the beam properties of a CO laser or a diode laser with a wavelength of 4-7 μm, for example. Since the relative humidity in an additive manufacturing process is similarly low to the preferred humidity values, it is advantageous to calibrate the energy beam under these conditions as well. Preferably, a temperature of the gas during calibration is at least 10° C. and/or at most 50° C.

By contrast, a typical relative ambient humidity prevails in the remaining volume of the process chamber of the additive manufacturing device during the flow into the hollow space and is preferably greater than 3% on average, further preferably greater than 5%, still further preferably greater than 10%, particularly preferably greater than 20%.

The hollow space of the calibration system, i.e. the volume between the beam inlet, the calibration aid and the measuring instrument, does not have to be gas-tight. Preferably, it has small gaps, e.g. at the connection points between the individual elements, through which the gas can flow out. This advantageously displaces the gas composition of the ambient atmosphere from the hollow space, particularly when the hollow space is first flooded with the gas.

The gas is preferably provided by the gas supply of the additive manufacturing device. This is advantageous as the same gas is used directly as in the manufacturing process and therefore substantially the same optical conditions prevail as in the process gas atmosphere.

The gas is preferably introduced into the hollow space via a separate connection or inlet in the process chamber. This means that an additional gas connection or gas inlet for the calibration is preferably arranged in the process chamber. For calibration, it is therefore preferable not to use one or more existing gas inlets in the process chamber, which are used for relatively large-volume inertisation and/or cleaning of the process chamber volume of impurities in the process gas. The inlets for the manufacturing process therefore do not need to be adjusted. In addition, the separate connection for calibration can preferably be actuated or controlled independently of the other inlets. For example, the previously mentioned relative humidity values in the hollow space can also be achieved thanks to the adjustable volume flow of the gas for calibration.

According to an alternative preferred embodiment, a number of existing gas inlets in the process chamber are used to provide the gas that is suitable for calibration. For this purpose, the gas is preferably supplied to the additive manufacturing device by means of an inflow device assigned to a number of jet inlets. In regular manufacturing operation, the inflow device or purging device is used for the directed inflow of at least one beam inlet or laser window or coupling window. To perform the calibration, the inflow device is activated and controlled or actuated separately, while other devices for global flooding/flowing of the process chamber with process gas/inert gas can be deactivated at the same time. The inflow device therefore supplies the inflow opening of the calibration aid with the gas that is suitable for the calibration to perform the calibration.

For example, the hollow space of the calibration aid can be docked to an opening (gas inlet) of the inflow device on the process chamber side in the intended position and direct the gas into the area between the beam inlet or coupling window and the measuring unit during calibration. Relative gas tightness can be achieved, for example, by designing the calibration aid to complement the geometry of the ceiling wall in certain areas. This means that, due to its shape, the calibration aid adjoins the wall or ceiling wall of the process chamber substantially gas-tightly—e.g. through appropriate positioning and manufacturing accuracy and/or by means of additional seals.

The calibration aid preferably forms the hollow space in an intended position in co-operation with a process chamber wall of the additive manufacturing device. The inflow opening of the calibration aid is particularly preferably located at a gas outlet opening of the inflow device and is fluidically connected to it.

The hollow space thus serves as a gas duct or as a gas channel and can be implemented, for example, by recesses or a design of the calibration aid which, in the intended position, comprises surfaces that are spaced apart from the process chamber wall in certain areas. In the intended docked state on the inflow device and/or on a process chamber ceiling and/or wall, the calibration aid according to the invention can form the hollow space, i.e. a gap or channel through which the flow passes, with the measuring unit. The hollow space formed in this way can have an outflow opening which, during intended operation, is the only opening of the calibration aid that allows the inflowing gas to escape into the interior of the process chamber.

An advantageous synergy effect results from the fact that such inflow devices are generally arranged on a ceiling wall of the process chamber and in the vicinity of the existing number of beam inlets or coupling windows. Their use in the method or calibration system according to the invention therefore serves a further purpose outside the manufacturing process, so that any additional connections, valves and/or conduits that may otherwise be required are advantageously saved.

The hollow space preferably has a variable height. In other words, the distance between the beam inlet and the measuring unit can be set or adjusted by means of the hollow space, in particular by means of the elements that form the hollow body. This allows, for example, the beam properties of the energy beam to be calibrated in different height positions of the manufacturing plane or the construction field. Detailed embodiments are described below.

In order to vary the height, the hollow space is preferably designed to be expandable. For this purpose, the hollow space, i.e. in particular the hollow body, can preferably be made of an elastic material, in particular as a hose. Alternatively or additionally, it can particularly preferably be designed as a bellows or similarly stretchable element. At the very least, the hollow body preferably has correspondingly stretchable areas. This design allows the height position of the measuring unit to be varied, as well as the position within the manufacturing plane perpendicular to the height.

Furthermore, the hollow space or the hollow body can be designed particularly preferably as an elastic tent or as a tent in the form of a bellows. It can have a pyramid or cone shape, for example. In contrast to a substantially linear or tubular design of the hollow body, a tent-like, pyramid-shaped or cone-shaped design makes it possible to carry out calibration measurements over the entire construction field without repositioning the calibration aid.

In order to vary the height, the hollow space or hollow body is alternatively or additionally preferably designed to be extendable. In other words, it has at least one extendable part or an extension. It can also comprise rigid components. The extension can be a telescopic extension, for example.

Preferably, the calibration aid has a joint at at least one, particularly preferably at each, end of the hollow body. The joint can be a simple swivel joint or a combination of several joints, for example. The joint can also be bellows-like, for example. However, the joint is particularly preferably designed as a ball joint. By means of the joint, especially in combination with the variable height of the hollow space or hollow body, the measuring unit can be positioned advantageously at different positions in the manufacturing plane, especially at different positions required for calibration, with any height settings of the manufacturing plane. The beam path remains surrounded by the hollow body or surrounded in its hollow space so that the energy beam, during calibration, passes through the gas that is suitable for calibration.

The calibration aid is preferably designed to be self-retaining. This means that it is preferably designed in such a way that it retains a height and/or joint position once it has been set. The calibration aid is therefore particularly preferably designed to be self-retaining in such a way that it remains fixed in position and/or dimensionally stable in the additive manufacturing device.

This is achieved, for example, by creating frictional resistance between the individual adjustable elements. The frictional resistance can be generated by a relatively small clearance and/or corresponding surface properties, in particular by a suitable surface roughness of the elements. The frictional resistance is preferably easy to overcome during manual adjustment, but is sufficient for the individual elements to maintain their relative position or arrangement without external influence.

The calibration system preferably has fastening means for attaching the calibration aid to the additive manufacturing device. The fastening means are arranged, for example, on the calibration aid or the additive manufacturing device. They are preferably designed as complementary elements that form a form fit and/or frictional engagement. The calibration aid can be implemented, for example, with the aid of clamping screws or a clip fastener, in particular by means of manually releasable, form-fit latching lugs, other form-fit elements and/or the like. The calibration aid is preferably fastened in the area of the beam entry into the process chamber or coupling window for the energy beam.

In the additive manufacturing device, the calibration aid preferably extends over a partial or complete distance between a manufacturing plane or the construction field and a beam inlet of the additive manufacturing device. This means that the calibration aid is attached to the coupling window, for example, as described above, but does not extend completely from there to the manufacturing plane, but holds the measuring unit—virtually floating—in a position between the manufacturing plane and the beam inlet.

The hollow body of the calibration aid preferably completely surrounds the energy beam from the position where the energy beam passes through the beam inlet or the coupling window until it hits the measuring unit. The volume surrounded by the hollow body, i.e. the hollow space, is preferably smaller than the volume of the process chamber, in particular smaller than a third, more preferably smaller than a quarter, even more preferably smaller than a tenth, particularly preferably smaller than a fiftieth, very particularly preferably smaller than a hundredth of the volume of the process chamber. The ratio and the resulting savings effect continue to improve with increasing size of the construction space. Accordingly, the time required for flooding the volume for calibration according to the invention is also advantageously shorter.

The calibration aid and/or the measuring unit are preferably removable from the process chamber and are removed from the process chamber before an additive manufacturing process. This means that before start of operation of the additive manufacturing device or after a preceding additive manufacturing process, a calibration according to the invention is preferably carried out, the calibration aid and/or the measuring unit is then preferably removed from the process chamber, and a new, subsequent additive manufacturing process is then carried out.

This means that an additive manufacturing process preferably does not take place during calibration. As a result, the flow to the process chamber, which can be provided, for example, by a circulation system for supplying and returning process gas, possibly with filtering of contaminated process gas, is particularly preferably deactivated during calibration with the calibration system according to the invention. This advantageously saves process gas or the energy required to circulate the process gas.

The property of the energy beam, which is recorded for calibration, preferably comprises a beam power, an intensity distribution, a focus position, a focus geometry and/or a response behaviour of the energy beam. Alternatively or additionally, properties of an energy beam deflection device (e.g. a galvanometer scanner) can also be measured, e.g. the positional accuracy of one or more deflection devices relative to each other.

A typical power meter is used to determine the laser power, for example, as described above. The laser power is preferably not measured in the focal point or focus, but outside the focus, as the intensity in the focus may be too high at certain points. If the focal point is in the manufacturing plane, for example, the power meter is simply placed on the manufacturing plane or a construction platform. The offset to the focal point created in this way is sufficient for the power measurement, as the power meter can still measure the entire power in this way without the intensity being too high at one point.

The focus position indicates the position of the focus in three-dimensional space in relation to the additive manufacturing device, i.e. in particular a height above the manufacturing plane or a distance to the beam inlet as well as a two-dimensional position in a plane parallel to the manufacturing plane. The focus geometry indicates whether the focus is circular, elliptical, in particular with an indication of the main axes, or otherwise shaped. The focus position and the focus geometry can be determined, for example, using a focus monitor as a measuring unit. This can be realised in a simple way, for example, by means of a power meter with a pinhole (dot-shaped aperture) in front of it.

The response behaviour of the energy beam describes a reaction delay or power curve when switching on, switching off or when the power requirement changes. Thermal paper, for example, can be used as a measuring unit for the response behaviour. The corresponding properties of the response behaviour can be determined after the calibration measurements.

With reference to, an additive manufacturing devicefor a three-dimensional object is described below. The manufacturing deviceshown schematically and partially in section inis a selectively acting laser melting device. To build up an object, it contains a process chamberwith a chamber wall.

An upwardly open containerwith a container wallis arranged in the process chamber. A manufacturing planeis defined by the upper opening of the container, wherein the area of the manufacturing planewithin the opening that can be used to build the objectis referred to as the construction area. In addition, the process chambercomprises a process gas supplyassociated with the process chamberand a process gas outlet.

In the containerthere is arranged a carriermovable in a vertical direction V, to which a base plateis attached, which closes the containerat the bottom and thus forms its base. The base platecan be a plate formed separately from the carrier, which is attached to the carrier, or it can be formed integrally with the carrier. Depending on the powder and process used, a construction platformcan also be attached to the base plateas a construction base on which the objectis built. However, the objectcan also be built on the base plateitself, which then serves as a construction base. In, the objectto be formed in the containeron the construction platformis shown below the working planein an intermediate state with several solidified layers surrounded by unsolidified build-up material.